Retirement and Other Benefit Programs (Summary of Amounts Recorded in AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
US | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
(Loss)/gain arising during the year	$ (14.9)	$ 83.4
Reclassification of gain to income statement	0.0	(69.4)
Pension and other employee benefit (loss)/gain, pre-tax	(14.9)	14.0
US | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
(Loss)/gain arising during the year	10.1	0.1
Reclassification of gain to income statement	0.0	0.0
Pension and other employee benefit (loss)/gain, pre-tax	10.1	0.1
International | Pensions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
(Loss)/gain arising during the year	41.2	(10.3)
Reclassification of gain to income statement	(1.3)	0.0
Pension and other employee benefit (loss)/gain, pre-tax	$ 39.9	$ (10.3)